1. Field of the Invention
The present invention relates to a thin-film-transistor (TFT) technology field, and more particularly to a TFT device for measuring a contact resistance and measurement method for a contact resistance.
2. Description of Related Art
A Thin-Film-Transistor (TFT) is widely applied in a semiconductor industry, a display industry, a transducer industry and a chip industry. The research for the field effect transistor mainly includes stability and functionality.
A TFT is a triode, which includes a gate electrode, a source electrode and a drain electrode. When a gate voltage is greater than a threshold voltage (Vth), an active layer generates a carrier gathering and an energy band bending under the function of the gate voltage in order to form a conductive channel. At this time, when a non-zero voltage is applied between the source electrode and the drain electrode, the carrier can move in a predetermined direction in the conductive channel under the function of the non-zero voltage in order to form a current. The above is the basic operation principle of the TFT device.
According to a physics formula: I=U/R, when a voltage is fixed, the resistance is greater, and the current is smaller. In the research of the TFT device, how to obtain a conduction current having a greater current under a lower Vds is always a key problem. To achieve the above purpose, decreasing a resistance between the source electrode and the drain electrode as many as possible is required. Because the source electrode and the drain electrode are made of a metal material generally, and a semiconductor material is generally a non-metal material, an interface between the source electrode and a semiconductor and an interface between the drain electrode and the semiconductor exist a contact resistance. The contact resistance is decided based on a treatment for the interface and a difference in energy functions of a metal material and a semiconductor material. Accordingly, the mechanisms of a channel resistance and the contact resistance are different. In a research, the channel resistance and the contact resistance are studied separately. However, when a TFT device is finished, the channel resistance and the contact resistance are integrated, according to an I-V (current-voltage) curve, a sum of the channel resistance and the contact resistance is obtained:RTotal=RC+RL, RL=kL (k is a constant) Rtotal=Rc+kL=Vds/Ids 
Wherein, RC is the contact resistance, RL is the channel resistance, L is a length of the channel of the TFT. Utilizing the above formula, measuring TFT devices having different L, and finally, drawing a RTotal-L diagram, an intercept on a vertical axis of a straight line is the RC (as shown in FIG. 1). The above method is called a TLM (The Transmission Line Modeling Method) method.
In the conventional art, when utilizing the TLM method to obtain the contact resistance, multiple TFT devices having different lengths (L) have to be manufactured (as shown in FIG. 2). Therefore, a uniformity for manufacturing the TFT devices will affect the final result. A distribution region of the TFT devices is larger, an occupied experimental region is larger, and a utilization of the experimental region is lower. Manufacturing multiple TFT devices relates to an affection of the interface status and the repeatability of the manufacturing process.